The present invention generally relates to a method and materials for mercury capture. More specifically, the present invention relates to a method and materials for capturing mercury using sorbent materials.
Mercury is considered by the government to be an air toxic pollutant. Mercury is of significant environmental concern because of its toxicity, persistence in the environment, and bioaccumulation in the food chain. Elemental mercury is volatile and is therefore released as a vapor into the environment from a variety of anthropogenic sources. Atmospheric deposition of mercury is reported to be the primary cause of elevated mercury levels in fish found in water bodies remote from known sources of this heavy metal.
Mercury can enter into the environment through the disposal (e.g., landfilling, incineration) of certain products. Products containing mercury include: auto parts, batteries, fluorescent lamps, medical products, thermometers, flat-panel televisions and thermostats. Due to health concerns, toxic use reduction efforts are cutting back or eliminating mercury in such products. For example, most thermometers now use pigmented alcohol instead of mercury.
Fluorescent lamps are mercury-vapor electric discharge lamps, and most contain from 1 to 10 mg of mercury depending upon the type of fluorescent lamp. Much of the mercury in new lamps is in the elemental state and being volatile can be released into the atmosphere when the fluorescent lamp is broken.
Currently, 300 million CFLs (compact fluorescent lamps) are sold per year. In the U.S., projections suggest that there will be at least 3 billion CFLs in U.S. homes in five years with an ultimate capacity of 4 billion. The main cause for the increase in sale of these CFLs containing mercury is their energy efficiency.
Broken CFLs can pose an immediate health hazard due to the evaporation of mercury into room air. Inhalation exposure is a concern as 80% of inhaled mercury is physiologically absorbed.
Currently, there is no reliable method or device for capturing and stabilizing mercury found in consumer products, such as CFLs. CFLs are being disposed of by consumers by a variety of methods across the United States. Many consumers have the option of disposing of these products in the same way they dispose of other solid waste. The EPA has reported CFLs are being disposed in municipal waste landfill, recycling centers, municipal waste incineration, and hazardous waste disposal.
Most florescent bulb recyclers in the United State employ the dry recycling process which generates four products: mercury-contaminated phosphor powder, mercury-contaminated filters, crushed glass, and aluminum end caps. The dry recycling process is a system which operates under negative pressure to minimize mercury emissions to the atmosphere. The spent CFLs are first broken. During crushing, a vacuum system collects the mercury vapor and the crushed materials including phosphor powder which contains most of the mercury. The mercury vapor is usually captured by carbon filters during crushing. Mercury-contaminated phosphor powder and carbon filters are placed in a retort to vaporize the mercury and collect it for reuse. The separation process employed by most lamp recyclers cannot remove phosphor powder and mercury on lamp glass completely. See M. Jang et al., “Characterization and capturing of mercury from spent fluorescent lamps,” Waste Management, Vol. 25 (2005).
Three processes are most important for the decontamination of CFL residues: (i) a thermal process (ii) a chemical process involving lixiviation by aqueous solutions and (iii) stabilization. The complexity of these processs, the necessity of multiple steps, the utilization of chemical reagants, and especially the generation of effluents that require adequate treatment are the disadvantages of these processes. See W. A. Durão Jr. et al., “Mercury Reduction studies to facilitate the thermal decontamination of phosphor powder residues from spent fluorescent lamps”, Waste Management (2007).
The U.S. Environmental Protection Agency recommends that, in the absence of local guidelines, fluorescent bulbs be double-bagged in plastic bags before disposal. The used or broken CFLs are placed in two plastic bags and put it in the outside trash, or other protected outside location, for the next normal trash collection. However, the double-bagging of broken CFLs will not prevent the release of mercury vapor into the air when the bulbs are compromised according to recent data from the Maine Department of Environmental Management.
In addition, there is no reliable and efficient method for cleaning up accidentally broken CFLs in a consumer's home. Today, if a CFL is broken, the shards of glass can be picked up by hand but some mercury-containing phosphor typically spills onto the surface causing the breakage site to continue to emit mercury into the air for hours or days causing a potential health risk, especially in the case of pregnant women or young children.
It would therefore be desirable to provide a method of safely and effectively disposing of mercury-containing products, such as CFLs. In addition, there is a need to capture and stabilize volatile mercury to prevent its release into room air when consumer products such as CFLs are broken. Finally, there is a need to provide materials or methods to allow for the safe disposal of the various pieces of broken consumer products such as CFLs.